G.f. = b(2)*b(4)*b(6)/(x^8+x^6-x^5+x^4-2*x^3-x+1), where b(k) = (1-x^k)/(1-x).

Terms

a(0) =1a(1) =4a(2) =9a(3) =18a(4) =33a(5) =56a(6) =93a(7) =151a(8) =241a(9) =383a(10) =606a(11) =956a(12) =1506a(13) =2369a(14) =3724a(15) =5852a(16) =9193a(17) =14439a(18) =22676a(19) =35609a(20) =55916a(21) =87801a(22) =137865a(23) =216473a(24) =339899a(25) =533696a(26) =837986a(27) =1315766a(28) =2065951a(29) =3243852